TedEd-06

The Hidden Network that Makes
the Internet Possible

In 2012, a team of Japanese and Danish researchers set a world record, transmitting 1 petabit ofdata — that’s 10,000 hours of high-def video — over a fifty-kilometer cable, in a second. This wasn’t
just any cable. It was a souped-up version of fiber optics — the hidden network that links our planet
and makes the internet possible.
For decades, long-distance communications between cities and countries were carried by electricalsignals, in wires made of copper. This was slow and inefficient, with metal wires limiting data rates
and power lost as wasted heat. But in the late 20th century, engineers mastered a far superior
method of transmission. Instead of metal, glass can be carefully melted and drawn into flexible fiber
strands, hundreds of kilometers long and no thicker than human hair. And instead of electricity,
these strands carry pulses of light, representing digital data. But how does light travel within glass,rather than just pass through it? The trick lies in a phenomenon known as total internal reflection.
Since Isaac Newton’s time, lens makers and scientists have known that light bends when it passes

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The Hidden Network that Makes
the Internet Possible

between air and materials like water or glass. When a ray of light inside glass hits its surface at asteep angle, it refracts, or bends as it exits into air. But if the ray travels at a shallow angle, it’ll bend
so far that it stays trapped, bouncing along inside the glass. Under the right condition, something
normally transparent to light can instead hide it from the world.
Compared to electricity or radio, fiber optic signals barely degrade over great distances — a littlepower does scatter away, and fibers can’t bend too sharply, otherwise the light leaks out. Today, asingle optical fiber carries many wavelengths of light, each a different channel of data. And a fiber
optic cable contains hundreds of these fiber strands. Over a million kilometers of cable crisscross
our ocean floors to link the continents — that’s enough to wind around the Equator nearly thirty
times. With fiber optics, distance hardly limits data, which has allowed the internet to evolve into aplanetary computer.
Increasingly, our mobile work and play rely on legions of overworked computer servers, warehousedin gigantic data centers flung across the world. This is called cloud computing, and it leads to two
big problems: heat waste and bandwidth demand. The vast majority of internet traffic shuttles
around inside data centers, where thousands of servers are connected by traditional electricalcables. Half of their running power is wasted as heat. Meanwhile, wireless bandwidth demand
steadily marches on, and the gigahertz signals used in our mobile devices are reaching their datadelivery limits. It seems fiber optics has been too good for its own good, fueling overly-ambitious
cloud and mobile computing expectations. But a related technology, integrated photonics, has cometo the rescue.
Light can be guided not only in optical fibers, but also in ultrathin silicon wires. Silicon wires don’t
guide light as well as fiber. But they do enable engineers to shrink all the devices in a hundred
kilometer fiber optic network down to tiny photonic chips that plug into servers and convert theirTedEd-06

The Hidden Network that Makes
the Internet Possible

electrical signals to optical and back. These electricity-to-light chips allow for wasteful electricalcables in data centers to be swapped out for power-efficient fiber. Photonic chips can help break
open wireless bandwidth limitations, too. Researchers are working to replace mobile gigahertz
signals with terahertz frequencies, to carry data thousands of times faster. But these are short-range
signals: they get absorbed by moisture in the air, or blocked by tall buildings. With tiny wireless-tofiber photonic transmitter chips distributed throughout cities, terahertz signals can be relayed overlong-range distances. They can do so via a stable middleman, optical fiber, and make hyperfast
wireless connectivity a reality.
For all of human history, light has gifted us with sight and heat, serving as a steady companion while
we explored and settled the physical world. Now, we’ve saddled light with information and redirected
it to run along a fiber optic superhighway — with many different integrated photonic exits— to build
an even more expansive, virtual world.